The present invention relates to an alarm sensing arrangement and, more particularly, to an alarm sensing loop in which some of the alarm sensors (fixed) are continuously surpervised and others of the alarm sensors (movable) may be selectively supervised.
The monitoring of alarm sensors in buildings can be accomplished either by a central station which is located remotely from the building or an alarm panel which is located locally within the building. The typical central station is connected to many buildings throughout a town or city and monitors either the current levels on direct wired systems in which a pair of wires is specifically dedicated to connecting the central station to a single customer's premises or the codes which identify which customer of a plurality of customers connected by a pair of wires to the central station is providing an alarm. The operator of the central station then watches the current levels or codes and will contact local police or security forces in the event of alarm conditions. The local panel, however, provides local alarm indications at the customer's premises and may or may not be tied into police stations.
All of the systems discussed above typically utilize alarm loops located within the customer's premises. Such alarm loops usually comprise a plurality of alarm sensors which may, for example, include switches for sensing the opening of doors and windows, and/or strip sensors which are, in effect, normally closed switches for sensing the breakage or cutting of the glass of windows or doors. Some of these sensors must be supervised continuously regardless of the time of day whereas others of the sensors should not be supervised during certain times of the day. For example, door switches are supervised only during hours of non-occupancy such that, if the building is not occupied, an opening of the supervised door switch will result in an alarm but an opening of the door during hours of occupancy will not result in an alarm. Other switches such as the sensing strips on windows should be supervised continuously so that a breakage thereof during hours of either occupancy or non-occupancy will result in an alarm.